Spatiotemporal epidemiology of cryptosporidiosis in the Republic of Ireland, 2008-2017: development of a space-time "cluster recurrence" index

Abstract

Background: Ireland frequently reports the highest annual Crude Incidence Rates (CIRs) of cryptosporidiosis in the EU, with national CIRs up to ten times the EU average. Accordingly, the current study sought to examine the spatiotemporal trends associated with this potentially severe protozoan infection.

Methods: Overall, 4509 cases of infection from January 2008 to December 2017 were geo-referenced to a Census Small Area (SA), with an ensemble of geo-statistical approaches including seasonal decomposition, Local Moran's I, and space-time scanning used to elucidate spatiotemporal patterns of infection.

Results: One or more confirmed cases were notified in 3413 of 18,641 Census SAs (18.3%), with highest case numbers occurring in the 0-5-year range (n = 2672, 59.3%). Sporadic cases were more likely male (OR 1.4) and rural (OR 2.4), with outbreak-related cases more likely female (OR 1.4) and urban (OR 1.5). Altogether, 55 space-time clusters (≥ 10 confirmed cases) of sporadic infection were detected, with three "high recurrence" regions identified; no large urban conurbations were present within recurrent clusters.

Conclusions: Spatiotemporal analysis represents an important indicator of infection patterns, enabling targeted epidemiological intervention and surveillance. Presented results may also be used to further understand the sources, pathways, receptors, and thus mechanisms of cryptosporidiosis in Ireland.

Keywords: Clustering; Cryptosporidiosis; Cryptosporidium; Seasonality; Space–time scanning; Spatiotemporal epidemiology.

Fig. 1

Geographical zonation of the Republic of Ireland

Fig. 2

Age and gender distributions of cryptosporidiosis cases in the Republic of Ireland (2008–2017)

Fig. 3

Temporal distribution of cryptosporidiosis cases in Ireland (2008–2017)

Fig. 4

Seasonal decomposition of cryptosporidiosis in the Republic of Ireland (2008–2017), delineated by sporadic (left) and outbreak-related cases (right)

Fig. 5

Seasonal decomposition of travel-related cryptosporidiosis in the Republic of Ireland (2008–2017)

Fig. 6

Seasonal decomposition of cryptosporidiosis in the Republic of Ireland (2008–2017), delineated by epidemiologically relevant age sub-categories

Fig. 7

Seasonal decomposition of cryptosporidiosis in the Republic of Ireland (2008–2017), delineated by CSO urban/rural classification

Fig. 8

a Sporadic cryptosporidiosis case clusters and outliers determined by Anselin Local Moran’s I clusters b Outbreak-related cryptosporidiosis case clusters and outliers determined by Anselin Local Moran’s I clusters c Sporadic cryptosporidiosis case clusters and outliers among children aged 5 years and younger determined by Anselin Local Moran’s I clusters d Sporadic cryptosporidiosis case clusters and outliers among the cohort of people age 6 years and older determined by Anselin Local Moran’s I clusters

Fig. 9

a Sporadic cryptosporidiosis case hot and cold spots determined by Getis-Ord Gi* hot-spot analysis—b Outbreak-related cryptosporidiosis hot and cold spots determined by Getis-Ord Gi* hot-spot analysis—c Sporadic cryptosporidiosis case hot and cold spots among children aged 5 years and younger determined by Getis-Ord Gi* hot-spot analysis—d Sporadic cryptosporidiosis case hot and cold spots among the cohort of people age 6 years and older determined by Getis-Ord Gi* hot-spot analysis

Fig. 10

Space–time “cluster recurrence” index (0–10) for sporadic cryptosporidiosis cases in the Republic of Ireland, 2008–2017

Fig. 11

Space–time “cluster recurrence” index (0–10) for outbreak-related cryptosporidiosis cases in the Republic of Ireland, 2008–2017

Fig. 12

Space–time “cluster recurrence” index (0–10) for sporadic cryptosporidiosis cases in the Republic of Ireland, 2008–2017 (Delineated by epidemiologically relevant age category—Population ≤ 5 years)

Fig. 13

Space–time “cluster recurrence” index (0–10) for sporadic cryptosporidiosis cases in the Republic of Ireland, 2008–2017 (Delineated by epidemiologically relevant age category—Population > 5 years)